Deviated boreholes are drilled using whipstock assemblies. A whipstock is a device which can be secured in the casing of a well and which has a tapered, sloping upper surface that acts to guide well bore tools along the tapered surface and in a selected direction away from the straight course of the well bore.
To facilitate the use of a whipstock, a section of casing is used which has premilled window openings through which deviated well bores can be drilled. The whipstock can be positioned relative to the window using a landing system which comprises a plurality of stacked spacers mounted on a fixed mounting device at the bottom of the casing and defining at the top thereof a whipstock retaining receptacle, or by use of a latch between the whipstock and the casing. A stacked landing system can cause difficulty in aligning the whipstock with the window opening as the distance between the mounting device and the window increases. The whipstock may also turn during the drilling or setting processes resulting in the deviated well bore being directed incorrectly and/or the well bore tools being stuck in the wellbore. Sometimes a latch system is used to overcome some of these disadvantages. However, the latch can sometimes disengage between the whipstock and the casing, allowing the whipstock to turn or move down in the casing.
After the deviated wellbore is drilled, it can be left uncompleted or completed in any suitable way. To seal the deviated wellbore hydraulically from the main casing, a liner can be installed and cement can be pumped behind the liner. This is expensive and often creates obstructions in the main casing which complicates removal and run of the tools.
When the tools are used in horizontal primary bores, new problems arise. Running and retrieval tools which are useful for vertical tool manipulation are not always useful in horizontal applications.